Oxidative responses of human and murine macrophages during phagocytosis of Leishmania chagasi

Leishmania major infection in humanized mice induces systemic infection and provokes a nonprotective human immune response

Background

Leishmania (L.) species are the causative agent of leishmaniasis. Due to the lack of efficient vaccine candidates, drug therapies are the only option to deal with cutaneous leishmaniasis. Unfortunately, chemotherapeutic interventions show high toxicity in addition to an increased risk of dissemination of drug-resistant parasites. An appropriate laboratory animal based model is still missing which allows testing of new drug strategies in the context of human immune cells in vivo.

Methodology/Principal Findings

Humanized mice were infected subcutaneously with stationary phase promastigote L. major into the footpad. The human immune response against the pathogen and the parasite host interactions were analyzed. In addition we proved the versatility of this new model to conduct drug research studies by the inclusion of orally given Miltefosine. We show that inflammatory human macrophages get infected with Leishmania parasites at the site of infection. Furthermore, a Leishmania-specific human-derived T cell response is initiated. However, the human immune system is not able to prevent systemic infection. Thus, we treated the mice with Miltefosine to reduce the parasitic load. Notably, this chemotherapy resulted in a reduction of the parasite load in distinct organs. Comparable to some Miltefosine treated patients, humanized mice developed severe side effects, which are not detectable in the classical murine model of experimental leishmaniasis.

Conclusions/Significance

This study describes for the first time L. major infection in humanized mice, characterizes the disease development, the induction of human adaptive and innate immune response including cytokine production and the efficiency of Miltefosine treatment in these animals. In summary, humanized mice might be beneficial for future preclinical chemotherapeutic studies in systemic (visceral) leishmaniasis allowing the investigation of human immune response, side effects of the drug due to cytokine production of activated humane immune cells and the efficiency of the treatment to eliminate also not replicating (“hiding”) parasites.

As many as 12 million people suffer from Leishmania (L.) infection worldwide with about one to two million newly infected people every year. Due to the lack of vaccine strategies, the only option is chemotherapeutic intervention which can cause serious side effects. Therefore, new prevention or treatment strategies are urgently needed in addition to an appropriate animal model for testing. We infected humanized mice in the footpad with stationary phase promastigote L. major and analyzed the human innate and adaptive immune response by flow cytometry, histology, and quantitative PCR. Infected macrophages were detectable at the site of infection and in lymphoid organs. Additionally, we were able to measure Leishmania-specific T cell priming in humanized mice. However, these human immune defense mechanisms were not sufficient to prevent systemic spreading and lethality. By the inclusion of Miltefosine, we tested this novel model for its versatility in conducting drug studies. The oral treatment was able to reduce parasitic load but also revealed side effects which are described in humans but not in mice. Therefore, we propose humanized mice as a novel model, which offers the opportunity to study new therapy strategies in chronic leishmaniasis in the context of a human immune system.

Role of oxidative stress and apoptosis in the cellular response of murine macrophages uponLeishmaniainfection

Leishmaniaparasites are able to survive in the macrophage, one of the most hostile environments of the vertebrate host. The present study investigated howLeishmaniainfection influences these host cell defence mechanisms. Macrophages were infected with antimony-susceptible and -resistantLeishmaniastrains. Free radical production inLeishmania-infected macrophages was measured by electron paramagnetic resonance. Apoptosis was detected with fluorescence microscopy using Annexin-V FITC labelling and with Western blotting to detect caspase-3 cleavage. Independent of their drug susceptibility profile or species background, all studiedLeishmaniastrains induced a similar increase in free radical production in macrophages. O2●−production was significantly elevated during phagocytosis of the stationary phase promastigotes. Conversely, NO levels increased later in the infection and none of the strains induced capsase-3 cleavage.Leishmania donovaniinfection led to phosphatidylserine externalization only in RAW 264.7 cells. After an initial burst of O2●−during phagocytosis of promastigotes, amastigotes protect themselves by decreasing the O2●−production to the basal level. An increased NO production was observed 6 h after infection. Finally, induction of cell death is probably not essential in the survival of the parasite within the macrophage.

Phenelzine (monoamine oxidase inhibitor) increases production of nitric oxide and proinflammatory cytokines via the NF-κB pathway in lipopolysaccharide-activated microglia cells

Phenelzine is a potent monoamine oxidase inhibitor that is used in patients with depression. It is also well known that nitric oxide (NO) synthase inhibitors show preclinical antidepressant-like properties, which suggests that NO is involved in the pathogenesis of depression. The purpose of this study was to determine if phenelzine affects the production of NO and tumor necrosis factor-alpha (TNF-α) in activated microglia cells. BV-2 microglia cells and primary microglia cells were cultured in DMEM and DMEM/F12 and then cells were treated with LPS or LPS plus phenelzine for 24 h. The culture medium was collected for determination of NO, TNF-α, and IL-6 and cells were harvested by lysis buffer for Western blot analysis. Phenelzine increased the lipopolysaccharide (LPS)-induced expression of inducible nitric oxide synthase (iNOS), as well as the release of TNF-α and IL-6 in BV-2 microglia cells. It is also confirmed that phenelzine increased the levels of NO, TNF-α and IL-6 in LPS-activated primary microglia cells. Phenelzine increased nuclear translocation of NF-κB by phosphorylation of IκB-α in LPS-activated microglia cells. These findings suggest that high doses of phenelzine could aggravate inflammatory responses in microglia cells that are mediated by NO and TNF-α.

Receptor-mediated phagocytosis of Leishmania: implications for intracellular survival

The extracellular promastigote stage of Leishmania spp. is transmitted to mammals by a sand fly vector. Leishmania promastigotes ligate host macrophage receptors, triggering phagocytosis and subsequent internalization, a crucial step for survival. Parasites transform intracellularly to the amastigote stage. Many studies document different receptors detecting promastigotes and amastigotes, but the relative importance of each interaction is ill-defined. Recent studies suggest that the macrophage receptors utilized during phagocytosis impact the intracellular fate of the parasite. This review summarizes the receptors implicated in Leishmania phagocytosis over the past 30 years. It then proceeds to weigh the evidence for or against their potential roles in intracellular parasite trafficking.

Heme oxygenase-1 promotes the persistence of Leishmania chagasi infection

Visceral leishmaniasis (VL) remains a major public health problem worldwide. This disease is highly associated with chronic inflammation and a lack of the cellular immune responses against Leishmania. It is important to identify major factors driving the successful establishment of the Leishmania infection to develop better tools for the disease control. Heme oxygenase-1 (HO-1) is a key enzyme triggered by cellular stress, and its role in VL has not been investigated. In this study, we evaluated the role of HO-1 in the infection by Leishmania infantum chagasi, the causative agent of VL cases in Brazil. We found that L. chagasi infection or lipophosphoglycan isolated from promastigotes triggered HO-1 production by murine macrophages. Interestingly, cobalt protoporphyrin IX, an HO-1 inductor, increased the parasite burden in both mouse and human-derived macrophages. Upon L. chagasi infection, macrophages from Hmox1 knockout mice presented significantly lower parasite loads when compared with those from wild-type mice. Furthermore, upregulation of HO-1 by cobalt protoporphyrin IX diminished the production of TNF-α and reactive oxygen species by infected murine macrophages and increased Cu/Zn superoxide dismutase expression in human monocytes. Finally, patients with VL presented higher systemic concentrations of HO-1 than healthy individuals, and this increase of HO-1 was reduced after antileishmanial treatment, suggesting that HO-1 is associated with disease susceptibility. Our data argue that HO-1 has a critical role in the L. chagasi infection and is strongly associated with the inflammatory imbalance during VL. Manipulation of HO-1 pathways during VL could serve as an adjunctive therapeutic approach.

Serum myeloperoxidase activity and oxidative stress in patients with acute brucellosis

OBJECTIVES

The role of infection in the pathogenesis of atherosclerosis has been increasingly discussed. Previous studies have suggested that increased myeloperoxidase activity plays an important role in the pathogenesis of atherosclerosis. The aim of this study was to investigate the serum myeloperoxidase activity and catalase activity along with lipid hydroperoxide (LOOH) levels in patients with acute brucellosis.

DESIGN AND METHODS

Thirty-two patients with brucellosis and 33 healthy controls were enrolled. Serum myeloperoxidase activity, catalase activity and LOOH levels were determined.

RESULTS

Serum myeloperoxidase activity and LOOH levels were significantly higher in patients with brucellosis than controls (p<0.05, p<0.001), while catalase activity were significantly lower (p<0.001). LOOH levels were found to be significantly positively correlated with MPO activity (r=0.297, p=0.016) in patients.

CONCLUSIONS

These results indicate that increased myeloperoxidase activity and decreased catalase activity is associated with increased oxidative stress, which may have a role in atherosclerotic processes in brucellosis patients.

Relationship of oxidative stress in hepatitis B infection activity with HBV DNA and fibrosis

BACKGROUND

The aim of this study was to evaluate oxidative stress in various clinical forms of hepatitis B infection and to investigate its role in the development of the chronic form of the disease.

METHODS

Ninety-three patients with inactive hepatitis B surface antigen (HbsAg) carrier state (IHBCS), 65 patients with chronic hepatitis B infection (CHB), and 42 healthy adults were included in the study. The following values were measured and compared in patient groups: total antioxidant status (TAS), total oxidative stress (TOS), oxidative stress index (OSI), sulfhydryl (SH), lipid peroxidation (LOOH), catalase (CAT), and ceruloplasmin. In patients with chronic hepatitis B, these values were compared with HBV DNA and fibrosis levels.

RESULTS

ALT, TOS, LOOH, and OSI levels were higher in the CHB group compared to the other groups (P<0.001). Catalase levels increased in the CHB and IHBCS groups compared to the control group (P<0.001). Total aminooxidant and ceruloplasmin levels were found to be lowest in the CHB group and highest in the control group (P<0.001). Sulfhyrdyl was higher in the control group compared to the other groups (P<0.001). In the CHB group, there was no correlation between the HBV DNA and OSI (P>0.05).

CONCLUSIONS

These finding suggested that oxidative stress is associated with hepatitis B activity.

Analysis of the expression of toll-like receptors 2 and 4 and cytokine production during experimental Leishmania chagasi infection

Toll-like receptors (TLRs) recognise pathogen-derived molecules and influence immunity to control parasite infections. This study aimed to evaluate the mRNA expression of TLRs 2 and 4, the expression and production of the cytokines interleukin (IL)-12, interferon (IFN)-γ, tumor necrosis factor (TNF)-α, IL-17, IL-10 and transforming growth factor (TGF)-β and the production of nitric oxide (NO) in the spleen of mice infected with Leishmania chagasi. It also aimed to evaluate any correlations between mRNA expression TLR2 and 4 and cytokines and NO production. Infection resulted in increased TLR2-4, IL-17, TNF-α and TGF-β mRNA expression during early infection, with decreased expression during late infection correlating with parasite load. IFN-γ and IL-12 mRNA expression decreased at the peak of parasitism. IL-10 mRNA expression increased throughout the entire time period analysed. Although TGF-β, TNF-α and IL-17 were highly produced during the initial phase of infection, IFN-γ and IL-12 exhibited high production during the final phase of infection. IL-10 and NO showed increased production throughout the evaluated time period. In the acute phase of infection, there was a positive correlation between TLR2-4, TNF-α, IL-17, NO, IL-10 and TGF-β expression and parasite load. During the chronic phase of infection, there was a positive correlation between TLR2-4, TNF-α, IL-17 and TGF-β expression and parasite load. Our data suggest that infection by L. chagasi resulted in modulation of TLRs 2 and 4 and cytokines.

Killed but metabolically active Leishmania infantum as a novel whole-cell vaccine for visceral leishmaniasis

There are currently no effective vaccines for visceral leishmaniasis, the second most deadly parasitic infection in the world. Here, we describe a novel whole-cell vaccine approach using Leishmania infantum chagasi promastigotes treated with the psoralen compound amotosalen (S-59) and low doses of UV A radiation. This treatment generates permanent, covalent DNA cross-links within parasites and results in Leishmania organisms termed killed but metabolically active (KBMA). In this report, we characterize the in vitro growth characteristics of both KBMA L. major and KBMA L. infantum chagasi. Concentrations of S-59 that generate optimally attenuated parasites were identified. Like live L. infantum chagasi, KBMA L. infantum chagasi parasites were able to initially enter liver cells in vivo after intravenous infection. However, whereas live L. infantum chagasi infection leads to hepatosplenomegaly in mice after 6 months, KBMA L. infantum chagasi parasites were undetectable in the organs of mice at this time point. In vitro, KBMA L. infantum chagasi retained the ability to enter macrophages and induce nitric oxide production. These characteristics of KBMA L. infantum chagasi correlated with the ability to prophylactically protect mice via subcutaneous vaccination at levels similar to vaccination with live, virulent organisms. Splenocytes from mice vaccinated with either live L. infantum chagasi or KBMA L. infantum chagasi displayed similar cytokine patterns in vitro. These results suggest that KBMA technology is a potentially safe and effective novel vaccine strategy against the intracellular protozoan L. infantum chagasi. This approach may represent a new method for whole-cell vaccination against other complex intracellular pathogens.

Lulo cell line derived from Lutzomyia longipalpis (Diptera: Psychodidae): a novel model to assay Leishmania spp. and vector interaction

Background

Leishmania (Vianna) braziliensis, Leishmania (Leishmania) amazonensis and Leishmania (Leishmania) chagasi are important parasites in the scenario of leishmaniasis in Brazil. During the life cycle of these parasites, the promastigote forms adhere to the midgut epithelial microvillii of phlebotomine insects to avoid being secreted along with digestive products. Lulo cells are a potential model that will help to understand the features of this adhesion phenomenon. Here, we analyze the interaction between Leishmania spp. promastigotes and Lulo cells in vitro, specifically focusing on adhesion events occurring between three Leishmania species and this cell line.

Methods

Confluent monolayers of Lulo cells were incubated with promastigotes and adhesion was assessed using both light microscopy and scanning electron microscopy.

Findings

The results indicate that species from the subgenera Leishmania and Viannia have great potential to adhere to Lulo cells. The highest adherence rate was observed for L. (L.) chagasi after 24 h of incubation with Lulo cells (27.3 ± 1.8% of cells with adhered promastigotes), followed by L. (L.) amazonensis (16.0 ± 0.7%) and L. (V.) braziliensis (3.0 ± 0.7%), both after 48 h. In the ultrastructural analysis, promastigote adherence was also assessed by scanning electron microscopy, showing that, for parasites from both subgenera, adhesion occurs by both the body and the flagellum. The interaction of Lulo cells with Leishmania (L.) chagasi showed the participation of cytoplasmic projections from the former closely associating the parasites with the cells.

Conclusions

We present evidence that Lulo cells can be useful in studies of insect-parasite interactions for Leishmania species.

Alcohol-fermented soybean increases the expression of receptor-interacting protein 2 and IκB kinase β in mouse peritoneal macrophages

Soybean is a useful component of traditional Korean medicine with well-documented health-promoting effects. We investigated the effects of alcohol-fermented soybean (AFS) on immune function. When AFS treatment was used in combination with recombinant interferon-γ (rIFN-γ), there was a marked cooperative induction of nitric oxide (NO) and tumor necrosis factor (TNF)-α production in mouse peritoneal macrophages. AFS increased the expression of inducible NO synthase mRNA and protein in rIFN-γ-primed macrophages. Treating macrophages with pyrrolidine dithiocarbamate, an inhibitor of nuclear factor-κB (NF-κB), decreased the synergistic effects of AFS. In addition, AFS in combination with rIFN-γ increased the phosphorylation of p38 and c-Jun N-terminal kinase (JNK) but not extracellular signal-regulated kinase. However, AFS had no effect on phosphorylation of mitogen-activated protein kinases by itself. The p38 inhibitor SB203580 or the JNK inhibitor SP600125 inhibited the AFS-induced NO and TNF-α production. When AFS was used in combination with rIFN-γ, there was a co-operative activation of NF-κB and receptor-interacting protein 2 (Rip2)/IκB kinase (IKK)-β. Our results indicate that AFS increases the production of NO and TNF-α through the activation of Rip2/IKK-β in rIFN-γ-primed macrophages.

Evaluation of oxidative status in patients with Fasciola hepatica infection

BACKGROUND

F. hepatica infection is rare and mostly subclinical. Migration of juvenile forms of F. hepatica into the host's liver is accompanied by an inflammatory reaction followed by fibrosis and cirrhosis.

OBJECTIVE

The aim of this study was to evaluate oxidative status by using a novel automated method in patients with Fasciola hepatica.

METHODS

Twenty two patients with a diagnosis of F. hepatica and 26 healthy volunteers were enrolled in the study. Their Total antioxidant capacity status (TAC), total oxidant status (TOS) and catalase were measured in them and oxidative stress index (OSI) was calculated. These measurements were also taken for the control group and the values were compared.

RESULTS

Plasma levels of total TOS and OSI were significantly increased in patients as compared with healthy controls (P<0.001, P<0.001, P=0.001, P=0.008) respectively. In contrast, TAC level was significantly lower in patients as compared with controls (p<0.05). There was no significant difference between the catalase results of the two groups (p>0.05).

CONCLUSION

Total oxidative status and OSI were increased and total antioxidative status capacity was decreased in patients with F. hepatica infection. A high oxidative stress occurs during F. hepatica infection, which may cause severe damage in both the liver.

Leishmania-macrophage interactions: insights into the redox biology

Leishmaniasis is a neglected tropical disease that affects about 350 million individuals worldwide. The protozoan parasite has a relatively simple life cycle with two principal stages: the flagellated mobile promastigote living in the gut of the sandfly vector and the intracellular amastigote within phagolysosomal vesicles of the vertebrate host macrophage. This review presents a state-of-the-art overview of the redox biology at the parasite-macrophage interface. Although Leishmania species are susceptible in vitro to exogenous superoxide radical, hydrogen peroxide, nitric oxide, and peroxynitrite, they manage to survive the endogenous oxidative burst during phagocytosis and the subsequent elevated nitric oxide production in the macrophage. The parasite adopts various defense mechanisms to cope with oxidative stress: the lipophosphoglycan membrane decreases superoxide radical production by inhibiting NADPH oxidase assembly and the parasite also protects itself by expressing antioxidant enzymes and proteins. Some of these enzymes could be considered potential drug targets because they are not expressed in mammals. In respect to antileishmanial therapy, the effects of current drugs on parasite-macrophage redox biology and its involvement in the development of drug resistance and treatment failure are presented.

The effects of macrophage source on the mechanism of phagocytosis and intracellular survival of Leishmania

Leishmania spp. protozoa are obligate intracellular parasites that replicate in macrophages during mammalian infection. Efficient phagocytosis and survival in macrophages are important determinants of parasite virulence. Macrophage lines differ dramatically in their ability to sustain intracellular Leishmania infantum chagasi (Lic). We report that the U937 monocytic cell line supported the intracellular replication and cell-to-cell spread of Lic during 72 h after parasite addition, whereas primary human monocyte-derived macrophages (MDMs) did not. Electron microscopy and live cell imaging illustrated that Lic promastigotes anchored to MDMs via their anterior ends and were engulfed through symmetrical pseudopods. In contrast, U937 cells bound Lic in diverse orientations, and extended membrane lamellae to reorient and internalize parasites through coiling phagocytosis. Lic associated tightly with the parasitophorous vacuole (PV) membrane in both cell types. PVs fused with LAMP-1-expressing compartments 24 h after phagocytosis by MDMs, whereas U937 cell PVs remained LAMP-1 negative. The expression of one phagocytic receptor (CR3) was higher in MDMs than U937 cells, leading us to speculate that parasite uptake proceeds through dissimilar pathways between these cells. We hypothesize that the mechanism of phagocytosis differs between primary versus immortalized human macrophage cells, with corresponding differences in the subsequent intracellular fate of the parasite.

Role of cAMP Signaling in the Survival and Infectivity of the Protozoan Parasite, Leishmania donovani

Leishmania donovani, while invading macrophages, encounters striking shift in temperature and pH (from 22°C and pH 7.2 to 37°C and pH 5.5), which act as the key environmental trigger for differentiation, and increases cAMP level and cAMP-mediated responses. For comprehensive understanding of cAMP signaling, we studied the enzymes related to cAMP metabolism. A stage-specific and developmentally regulated isoform of receptor adenylate cyclase (LdRACA) showed to regulate differentiation-coupled induction of cAMP. The soluble acidocalcisomal pyrophosphatase, Ldvsp1, was the major isoform regulating cAMP level in association with LdRACA. A differentially expressed soluble cytosolic cAMP phosphodiesterase (LdPDEA) might be related to infection establishment by shifting trypanothione pool utilization bias toward antioxidant defense. We identified and cloned a functional cAMP-binding effector molecule from L. donovani (a regulatory subunit of cAMP-dependent protein kinase, LdPKAR) that may modulate metacyclogenesis through induction of autophagy. This study reveals the significance of cAMP signaling in parasite survival and infectivity.

Berberine chloride mediates its anti-leishmanial activity via differential regulation of the mitogen activated protein kinase pathway in macrophages

Background

A complex interplay between Leishmania and macrophages influences parasite survival and necessitates disruption of signaling molecules, eventually resulting in impairment of macrophage function. In this study, we demonstrate the immunomodulatory activity of Berberine chloride in Leishmania infected macrophages.

Principal Findings

The IC₅₀ of Berberine chloride, a quaternary isoquinoline alkaloid was tested in an amastigote macrophage model and its safety index measured by a cell viability assay. It eliminated intracellular amastigotes, the IC₅₀ being 2.8 fold lower than its IC₅₀ in promastigotes (7.10 µM vs. 2.54 µM) and showed a safety index >16. Levels of intracellular and extracellular nitric oxide (NO) as measured by flow cytometry and Griess assay respectively showed that Berberine chloride in Leishmania infected macrophages increased production of NO. Measurement of the mRNA expression of iNOS, IL-12 and IL-10 by RT-PCR along with levels of IL-12p40 and IL-10 by ELISA showed that in infected macrophages, Berberine chloride enhanced expression of iNOS and IL-12p40, concomitant with a downregulation of IL-10. The phosphorylation status of extracellular signal related kinase (ERK1/2) and p38 mitogen activated protein kinase (p38 MAPK) was studied by western blotting. In infected macrophages, Berberine chloride caused a time dependent activation of p38 MAPK along with deactivation of ERK1/2; addition of a p38 MAPK inhibitor SB203580 inhibited the increased generation of NO and IL-12p40 by Berberine chloride as also prevented its decrease of IL-10.

Conclusions

Berberine chloride modulated macrophage effector responses via the mitogen activated protein kinase (MAPK) pathway, highlighting the importance of MAPKs as an antiparasite target.

Fucoidan cures infection with both antimony-susceptible and -resistant strains of Leishmania donovani through Th1 response and macrophage-derived oxidants

OBJECTIVES

The aim of this study was to evaluate and characterize the antileishmanial efficacy of fucoidan, a polyanionic sulphated polysaccharide from brown algae, in experimental infections of BALB/c mice with antimony-susceptible (AG83) and -resistant (GE18ER) Leishmania donovani.

METHODS

The effect of fucoidan was assessed against intracellular parasites in cultured macrophages and in suppressing splenic and liver parasite burdens in a BALB/c mouse model of visceral leishmaniasis by microscopic evaluation of surviving intracellular amastigotes stained with Giemsa. To evaluate the type of immunological responses, real-time PCR and ELISA were performed for various Th1 and Th2 cytokines in both in vitro and in vivo infected conditions. To determine the effector mechanism, reactive oxygen species (ROS) and NO were measured in fucoidan-treated animals by H(2)DCFDA-based fluorometric analysis and Griess reaction, respectively.

RESULTS

In addition to having appreciable inhibitory effect on amastigote multiplication within macrophages (>93% inhibition at 50 μg/mL), complete elimination of liver and spleen parasite burden was achieved by fucoidan at a dose of 200 mg/kg/day given orally, 3 times weekly, in a 6-week mouse model of both antimony-susceptible and -resistant strains. This curative effect is associated with switching of T cell differentiation from Th2 to Th1 mode. Further, splenocytes of fucoidan-treated infected (AG83 and GE18FR) mice generated significantly enhanced levels of superoxide and NO. Not only was this treatment curative when administered orally 15 days post-infection, but it also imparted resistance to reinfection.

CONCLUSIONS

These results suggest the effectiveness of fucoidan as potent immunomodulator for controlling both antimony-susceptible and -resistant visceral leishmaniasis.

DETC induces Leishmania parasite killing in human in vitro and murine in vivo models: a promising therapeutic alternative in Leishmaniasis

Background

Chemotherapy remains the primary tool for treatment and control of human leishmaniasis. However, currently available drugs present serious problems regarding side-effects, variable efficacy, and cost. Affordable and less toxic drugs are urgently needed for leishmaniasis.

Methodology/Principal Findings

We demonstrate, by microscopy and viability assays, that superoxide dismutase inhibitor diethyldithiocarbamate (DETC) dose-dependently induces parasite killing (p<0.001) and is able to “sterilize” Leishmania amazonensis infection at 2 mM in human macrophages in vitro. We also show that DETC-induced superoxide production (p<0.001) and parasite destruction (p<0.05) were reverted by the addition of the antioxidant N-acetylcysteine, indicating that DETC-induced killing occurs through oxidative damage. Furthermore, ultrastructural analysis by electron microscopy demonstrates a rapid and highly selective destruction of amastigotes in the phagosome upon DETC treatment, without any apparent damage to the host cell, including its mitochondria. In addition, DETC significantly induced parasite killing in Leishmania promastigotes in axenic culture. In murine macrophages infected with Leishmania braziliensis, DETC significantly induced in vitro superoxide production (p = 0.0049) and parasite killing (p = 0.0043). In vivo treatment with DETC in BALB/C mice infected with Leishmania braziliensis caused a significant decrease in lesion size (p<0.0001), paralleled by a 100-fold decrease (p = 0.0087) in parasite burden.

Conclusions/Significance

Due to its strong leishmanicidal effect in human macrophages in vitro, its in vivo effectiveness in a murine model, and its previously demonstrated in vivo safety profile in HIV treatment, DETC treatment might be considered as a valuable therapeutic option in human leishmaniasis, including HIV/Leishmania co-infection.

Leishmania infantum: Lipophosphoglycan intraspecific variation and interaction with vertebrate and invertebrate hosts

Interspecies variations in lipophosphoglycan (LPG) have been the focus of intense study over the years due its role in specificity during sand fly-Leishmania interaction. This cell surface glycoconjugate is highly polymorphic among species with variations in sugars that branch off the conserved Gal(β1,4)Man(α1)-PO(4) backbone of repeat units. However, the degree of intraspecies polymorphism in LPG of Leishmania infantum (syn. Leishmania chagasi) is not known. In this study, intraspecific variation in the repeat units of LPG was evaluated in 16 strains of L. infantum from Brazil, France, Algeria and Tunisia. The structural polymorphism in the L. infantum LPG repeat units was relatively slight and consisted of three types: type I does not have side chains; type II has one β-glucose residue that branches off the disaccharide-phosphate repeat units and type III has up to three glucose residues (oligo-glucosylated). The significance of these modifications was investigated during in vivo interaction of L. infantum with Lutzomyia longipalpis, and in vitro interaction of the parasites and respective LPGs with murine macrophages. There were no consequential differences in the parasite densities in sand fly midguts infected with Leishmania strains exhibiting type I, II and III LPGs. However, higher nitric oxide production was observed in macrophages exposed to glucosylated type II LPG.

Leishmania inhibitor of serine peptidase 2 prevents TLR4 activation by neutrophil elastase promoting parasite survival in murine macrophages

Leishmania major is a protozoan parasite that causes skin ulcerations in cutaneous leishmaniasis. In the mammalian host, the parasite resides in professional phagocytes and has evolved to avoid killing by macrophages. We identified L. major genes encoding inhibitors of serine peptidases (ISPs), which are orthologs of bacterial ecotins, and found that ISP2 inhibits trypsin-fold S1A family peptidases. In this study, we show that L. major mutants deficient in ISP2 and ISP3 (Δisp2/3) trigger higher phagocytosis by macrophages through a combined action of the complement type 3 receptor, TLR4, and unregulated activity of neutrophil elastase (NE), leading to parasite killing. Whereas all three components are required to mediate enhanced parasite uptake, only TLR4 and NE are necessary to promote parasite killing postinfection. We found that the production of superoxide by macrophages in the absence of ISP2 is the main mechanism controlling the intracellular infection. Furthermore, we show that NE modulates macrophage infection in vivo, and that the lack of ISP leads to reduced parasite burdens at later stages of the infection. Our findings support the hypothesis that ISPs function to prevent the activation of TLR4 by NE during the Leishmania-macrophage interaction to promote parasite survival and growth.

LXR deficiency confers increased protection against visceral Leishmania infection in mice

Background

The liver X receptors (LXRs) are a family of nuclear receptor transcription factors that are activated by oxysterols and have defined roles in both lipid metabolism and cholesterol regulation. LXRs also affect antimicrobial responses and have anti-inflammatory effects in macrophages. As mice lacking LXRs are more susceptible to infection by intracellular bacteria Listeria monocytogenes and Mycobacterium tuberculosis, we hypothesized that LXR might also influence macrophage responses to the intracellular protozoan parasite Leishmania chagasi/infantum, a causative agent of visceral leishmaniasis.

Methods and Findings

Surprisingly, both LXRα knock-out and LXRα/LXRβ double-knock-out (DKO) mice were markedly resistant to systemic L. chagasi/infantum infection compared to wild-type mice. Parasite loads in the livers and spleens of these animals were significantly lower than in wild-type mice 28 days after challenge. Bone marrow-derived macrophages from LXR-DKO mice infected with L. chagasi/infantum in vitro in the presence of IFN-γ were able to kill parasites more efficiently than wild-type macrophages. This enhanced killing by LXR-deficient macrophages correlated with higher levels of nitric oxide produced, as well as increased gene expression of IL-1β. Additionally, LXR ligands abrogated nitric oxide production in wild-type macrophages in response to infection.

Conclusions

These observations suggest that LXR-deficient mice and macrophages mount antimicrobial responses to Leishmania infection that are distinct from those mounted by wild-type mice and macrophages. Furthermore, comparison of these findings to other intracellular infection models suggests that LXR signaling pathways modulate host antimicrobial responses in a complex and pathogen-specific manner. The LXR pathway thus represents a potential therapeutic target for modulating immunity against Leishmania or other intracellular parasites.

Leishmania spp. are protozoan single-cell parasites that are transmitted to humans by the bite of an infected sand fly, and can cause a wide spectrum of disease, ranging from self-healing skin lesions to potentially fatal systemic infections. Certain species of Leishmania that cause visceral (systemic) disease are a source of significant mortality worldwide. Here, we use a mouse model of visceral Leishmania infection to investigate the effect of a host gene called LXR. The LXRs have demonstrated important functions in both cholesterol regulation and inflammation. These processes, in turn, are closely related to lipid metabolism and the development of atherosclerosis. LXRs have also previously been shown to be involved in protection against other intracellular pathogens that infect macrophages, including certain bacteria. We demonstrate here that LXR is involved in susceptibility to Leishmania, as animals deficient in the LXR gene are much more resistant to infection with the parasite. We also demonstrate that macrophages lacking LXR kill parasites more readily, and make higher levels of nitric oxide (an antimicrobial mediator) and IL-1β (an inflammatory cytokine) in response to Leishmania infection. These results could have important implications in designing therapeutics against this deadly pathogen, as well as other intracellular microbial pathogens.

A controlled, randomized-blinded clinical trial to assess the efficacy of a nitric oxide releasing patch in the treatment of cutaneous leishmaniasis by Leishmania (V.) panamensis

A topical nanofiber nitric oxide (NO) releasing patch ( approximately 3.5 mumol NO/cm(2)/day for 20 days, NOP) was compared with intramuscular meglumine antimoniate (Glucantime, 20 mg/kg/day for 20 days) for the treatment of cutaneous leishmaniasis (CL) caused by Leishmania (V.) panamensis in Santander and Tolima, Colombia. A double-blind, randomized, placebo-controlled, clinical trial was conducted to determine whether the NOP is as effective as Glucantime for the treatment of CL. Patients were randomly assigned to Glucantime and placebo patches or NOP and placebo of Glucantime. The cure rates after a 3-month follow-up were 94.8% for the group that received Glucantime compared with 37.1% in the NOP group. Despite the lower efficacy of the NOP versus Glucantime, a significantly lower frequency of non-serious adverse events and a reduced variation in serum markers were observed in patients treated with NOP. Treatment of CL with NOP resulted in a lower effectiveness compared with Glucantime; however, the low frequency of adverse events and the facility of topic administration justify the development of new generations of NOP systems for the treatment of CL.

Leishmania major: anti-leishmanial activity of Nuphar lutea extract mediated by the activation of transcription factor NF-κB

Here we report the effect of a partially purified alkaloid fraction (NUP) of Nuphar lutea on nuclear factor kappa B (NF-κB) expression and studied its mechanism of toxicity against Leishmania major in C3H mice peritoneal macrophages. NUP was found to be a mixture of thermo-stable dimeric sesquiterpene thioalkaloids containing mainly thionupharidines. The anti-leishmanial activity was shown to be mediated through the activation of NF-κB and increased iNOS production. Additionally, the nitric oxide inhibitor, N(G)-monomethyl-L-arginine (0.5mM) totally reverted the anti-leishmanial effect of NUP (0.25 and 0.5μg/ml). NUP was also shown to act as an anti-oxidant, almost completely inhibiting the macrophage respiratory burst activity. However, no elevated lysozyme (EC3.2.1.17) or β-galactosidase (EC3.2.1.23) activities were demonstrated in macrophages treated with NUP. This study suggests, that the activity of NUP is mediated by NF-κB activation and the production of nitric oxide which is dependent on the L-arginine:NO pathway.

Evaluation of ex vivo human immune response against candidate antigens for a visceral leishmaniasis vaccine

People cured from visceral leishmaniasis (VL) develop protection mediated by Th1-type cellular responses against new infections. We evaluated cytokine responses against 6 defined candidate vaccine antigens in 15 cured VL subjects and 5 healthy endemic controls with no evidence of previous exposure to Leishmania parasites. Of the 6 cytokines examined, only interferon-gamma (IFN-gamma) differentiated cured VL patients from non-exposed individuals, with cured patients mounting a significantly higher IFN-gamma response to a crude parasite antigen preparation. Among candidate vaccine antigens tested, the largest number of cured subjects recognized cysteine proteinase B, leading to heightened IFN-gamma responses, followed by sterol 24-c-methyltransferase. These two antigens were the most immunogenic and protective antigens in a murine VL model, indicating a relationship between T cell recall responses of humans cured from VL and protective efficacy in an experimental model. Further studies may help prioritize antigens for clinical development of a subunit vaccine against VL.

Neutrophils and macrophages cooperate in host resistance against Leishmania braziliensis infection

Neutrophils play an active role in the control of infections caused by intracellular pathogens such as Leishmania. In the present study, we investigated the effect of neutrophil depletion at the time of Leishmania braziliensis infection of BALB/c mice and how neutrophils interact with the infected macrophage to promote parasite elimination. The in vivo depletion of neutrophils led to a significant increase in parasite load and enhanced the Th1-Th2 immune response in this experimental model of infection. BALB/c mice coinoculated with both parasites and live neutrophils displayed lower parasite burdens at the site of infection and in the draining lymph nodes. In vitro, we observed that live neutrophils significantly reduced the parasite load in L. braziliensis-infected murine macrophages, an effect not observed with Leishmania major. L. braziliensis elimination was dependent on the interaction between neutrophils and macrophages and was associated with TNF-alpha as well as superoxide production. Furthermore, cooperation between neutrophils and macrophages toward parasite elimination was also observed in experiments performed with L. braziliensis-infected human cells and, importantly, with two other New World Leishmania species. These results indicate that neutrophils play an important and previously unappreciated role in L. braziliensis infection, favoring the induction of a protective immune response.

Ex vivo and in vivo biological behavior of Leishmania (Viannia) shawi

Since the first description of Leishmania (Viannia) shawi, few studies were performed with this parasite. In the present work, the in vivo and ex vivo behavior of L. (Viannia) shawi infection was studied using murine model. Peritoneal macrophages from BALB/c and C57BL/6 mice were infected with promastigotes in the stationary phase of growth; after 24 h, the infection index and nitric oxide (NO) levels in the supernatant of the cultures were analyzed. BALB/c and C57BL/6 mice were infected into the hind footpad, and at each 2 weeks, mice were sacrificed, and the histological changes of the skin inoculation site, parasitism, and humoral immune responses were evaluated during 8 weeks. Ex vivo experiments showed that macrophages of BALB/c presented higher infection index and lesser NO levels than macrophages of C57BL/6. In vivo experiments showed that BALB/c presented higher lesion size than C57BL/6 mice; similarly, the histopathological changes and the parasitism in skin were more exacerbate in BALB/c mice. In draining lymph nodes, the main change was increase of germinative centers, and parasites were detected from 6 weeks pi onwards in both mice strain. IgG was detected in BALB/c mice from 4 weeks, while in C57BL/6, from 6 weeks pi onwards. Taken together, these results indicate that BALB/c showed a classical behavior of susceptibility when compared to C57BL/6 mice.

Overexpression of mitochondrial Leishmania major ascorbate peroxidase enhances tolerance to oxidative stress-induced programmed cell death and protein damage

Ascorbate peroxidase from Leishmania major (LmAPX) is one of the key enzymes for scavenging of reactive oxygen species generated from the mitochondrial respiratory chain. We have investigated whether mitochondrial LmAPX has any role in oxidative stress-induced apoptosis. The measurement of reduced glutathione (GSH) and protein carbonyl contents in cellular homogenates indicates that overexpression of LmAPX protects Leishmania cells against depletion of GSH and oxidative damage of proteins by H(2)O(2) or camptothecin (CPT) treatment. Confocal microscopy and fluorescence spectroscopy data have revealed that the intracellular elevation of Ca(2+) attained by the LmAPX-overexpressing cells was always below that attained in control cells. Flow cytometry assay data and confocal microscopy observation strongly suggest that LmAPX overexpression protects cells from H(2)O(2)-induced mitochondrial membrane depolarization as well as ATP decrease. Western blot data suggest that overexpression of LmAPX shields against H(2)O(2)- or CPT-induced cytochrome c and endonuclease G release from mitochondria and subsequently their accumulation in the cytoplasm. Caspase activity assay by flow cytometry shows a lower level of caspase-like protease activity in LmAPX-overexpressing cells under apoptotic stimuli. The data on phosphatidylserine exposed on the cell surface and DNA fragmentation results show that overexpression of LmAPX renders the Leishmania cells more resistant to apoptosis provoked by H(2)O(2) or CPT treatment. Taken together, these results indicate that constitutive overexpression of LmAPX in the mitochondria of L. major prevents cells from the deleterious effects of oxidative stress, that is, mitochondrial dysfunction and cellular death.

Proinflammatory cytokine and nitric oxide production by human macrophages stimulated with Trichomonas vaginalis

Trichomonas vaginalis commonly causes vaginitis and perhaps cervicitis in women and urethritis in men and women. Macrophages are important immune cells in response to T. vaginalis infection. In this study, we investigated whether human macrophages could be involved in inflammation induced by T. vaginalis. Human monocyte-derived macrophages (HMDM) were co-cultured with T. vaginalis. Live, opsonized-live trichomonads, and T. vaginalis lysates increased proinflammatory cytokines, such as TNF-alpha, IL-1beta, and IL-6 by HMDM. The involvement of nuclear factor (NF)-kappaB signaling pathway in cytokine production induced by T. vaginalis was confirmed by phosphorylation and nuclear translocation of p65 NF-kappaB. In addition, stimulation with live T. vaginalis induced marked augmentation of nitric oxide (NO) production and expression of inducible NO synthase (iNOS) levels in HMDM. However, trichomonad-induced NF-kappaB activation and TNF-alpha production in macrophages were significantly inhibited by inhibition of iNOS levels with L-NMMA (NO synthase inhibitor). Moreover, pretreatment with NF-kappaB inhibitors (PDTC or Bay11-7082) caused human macrophages to produce less TNF-alpha. These results suggest that T. vaginalis stimulates human macrophages to produce proinflammatory cytokines, such as IL-1, IL-6, and TNF-alpha, and NO. In particular, we showed that T. vaginalis induced TNF-alpha production in macrophages through NO-dependent activation of NF-kappaB, which might be closely involved in inflammation caused by T. vaginalis.

Increased DNA damage and oxidative stress in chickens with natural Marek's disease

Oxidative stress contributes to the accumulation of genomic abnormalities, prevents cellular apoptosis, and also mediates immunosuppression resulting in tumor formation. Marek's Disease provides excellent opportunities for the study of herpesvirus-induced tumors both in experimental- and natural conditions. The aim of this study was to examine the effects of Marek's Disease (MD) on basal levels of DNA strand breaks and on the oxidative-antioxidative status of chickens with MD. White-Lohmann hens-fifteen infected with Marek's Disease Virus (MDV) and fifteen healthy-of same age and sex were included in this study. MD infection was diagnosed via clinical signs, gross- and micro-pathological findings and also by detection of viral antigens in feather follicle epithelium by the indirect immunoperoxidase method. Compared with healthy controls, DNA damage was greater and levels of malondialdehyde (MDA) and plasma protein carbonyl (PCO), and plasma concentration of nitric oxide metabolites (NOx) higher in the MD group. Furthermore, total antioxidant activities (AOAs) were found lowered and glutathione (GSH) levels reduced in the MD group compared to the control group. Significantly positive correlation was found between DNA damage, MDA, PCO, and NOx in the MD group. DNA strand breaks were found negatively associated with AOA and GSH concentrations in the MD group. Our results demonstrated that oxidative stress markers and DNA damage substantially increased in chickens with MD, which indicated that increased DNA damage levels might be related to the increased oxidative stress and reduced antioxidant activity.

Nitric oxide production and nitric oxide synthase type 2 expression by cotton rat (Sigmodon hispidus) macrophages reflect the same pattern as human macrophages

Our knowledge of the antibacterial role of nitric oxide (NO) during infection is based on studies of murine macrophages, which secrete large amounts of NO. In contrast, human macrophages produce very little NO and its relevance as an antibacterial mediator during infection of humans is uncertain. We have defined bone marrow-derived macrophages from cotton rats (Sigmodon hispidus). These macrophages display phenotypical and functional characteristics similar to other rodent and human macrophages. The most interesting finding was the low level of NO production which is in contrast to findings for murine macrophages, but consistent with those of humans. In spite of these low levels, inhibition of NO production led to a decrease in killing of bacteria. Cotton rats are highly susceptible to a variety of human pathogens and therefore offer a rodent model of infectious diseases with similar characteristics to humans in terms of NO production.

IFN-beta impairs superoxide-dependent parasite killing in human macrophages: evidence for a deleterious role of SOD1 in cutaneous leishmaniasis

Type I IFNs (IFN-alpha/beta) have only recently gained considerable attention as immunomodulators in nonviral infectious diseases. IFN-beta has been shown to protect, in a NO-dependent manner, against murine Old World leishmaniasis caused by Leishmania major, but data in New World leishmaniasis are lacking. We found that IFN-beta dose-dependently increases parasite burden in Leishmania amazonensis- as well as Leishmania braziliensis-infected human macrophages, independent of endogenous or exogenous NO. However, IFN-beta significantly reduced superoxide release in Leishmania-infected as well as uninfected human macrophages. This decrease in superoxide production was paralleled by a significant IFN-beta-mediated increase in superoxide dismutase 1 (SOD1) protein levels. Additionally, IFN-beta inhibition of leishmanicidal activity was mimicked by SOD1 and antagonized by either pharmacological or small interfering RNA-mediated inhibition of SOD1. Finally, pronounced SOD1 expression in situ was demonstrated in biopsies from New World cutaneous leishmaniasis patients. These findings reveal a hitherto unknown IFN-beta/SOD1 axis in Leishmania infection and suggest that inhibition of SOD-associated pathways could serve as strategy in the treatment of L. amazonensis as well as L. braziliensis infection, major human pathogens.

The role of reduced pterins in resistance to reactive oxygen and nitrogen intermediates in the protozoan parasite Leishmania

During its life cycle, the protozoan parasite Leishmania experiences oxidative stress when interacting with macrophages. Reduced pterins are known scavengers of reactive oxygen and nitrogen intermediates. Leishmania has a pteridine reductase, PTR1, whose main function is to provide reduced pterins. We investigated the role of PTR1 in resistance to oxidative and nitrosative stress in Leishmania tarentolae, Leishmania infantum, and Leishmania major PTR1(-/-) mutants. The PTR1(-/-) cells of the three species were more sensitive to H2O2- and NO-induced stress. Using a fluorescent probe allowing ROI quantification, we demonstrated an increase in intracellular oxidant molecules in the PTR1(-/-) mutants. The disruption of PTR1 increased metacyclogenesis in L. infantum and L. major. We purified metacyclic parasites from PTR1(-/-) mutants and control cells and tested their intracellular survival in the J774 mouse cell line and in human monocyte-derived macrophages. Our results showed that PTR1(-/-) null mutants survived less in both macrophage models compared to control cells and this decrease was more pronounced in macrophages activated for oxidant production. This study demonstrates that one physiological role of reduced pterins in Leishmania is to deal with oxidative and nitrosative species, and a decreased ability to provide reduced pterins leads to decreased intracellular survival.

The cytosolic tryparedoxin of Leishmania infantum is essential for parasite survival

Leishmania infantum cytosolic tryparedoxin (LiTXN1) can be regarded as a potential candidate for drug targeting. This redox active molecule, which belongs to the thioredoxin superfamily, is one constituent of the hydroperoxide elimination cascade in L. infantum and may also be involved in other cellular processes such as DNA synthesis or host-parasite interaction. In order to validate LiTXN1 as a drug target we have employed a gene replacement strategy. We observed that substitution of both chromosomal LiTXN1 alleles was only possible upon parasite complementation with an episomal copy of the gene. Furthermore, contrary to control parasites carrying the empty vector, both the insect and the mammalian stages of L. infantum retained the episomal copy of LiTXN1 in the absence of drug pressure. These results confirm the essentiality of LiTXN1 throughout the life cycle of the parasite, namely in the disease-causing amastigote stage. In addition, the data obtained showed that disruption of one allele of this gene leads only to a 25% reduction in the expression of LiTXN1. Even though this does not affect promastigote growth and susceptibility to hydrogen peroxide, ex vivo infection assays suggest that wild-type levels of LiTXN1 are required for optimal L. infantum virulence.

Control of parasitophorous vacuole expansion by LYST/Beige restricts the intracellular growth of Leishmania amazonensis

The intracellular protozoan Leishmania replicates in parasitophorous vacuoles (PV) that share many features with late endosomes/lysosomes. L. amazonensis PVs expand markedly during infections, but the impact of PV size on parasite intracellular survival is still unknown. Here we show that host cells infected with L. amazonensis upregulate transcription of LYST/Beige, which was previously shown to regulate lysosome size. Mutations in LYST/Beige caused further PV expansion and enhanced L. amazonensis replication. In contrast, LYST/Beige overexpression led to small PVs that did not sustain parasite growth. Treatment of LYST/Beige over-expressing cells with vacuolin-1 reversed this phenotype, expanding PVs and promoting parasite growth. The opposite was seen with E-64d, which reduced PV size in LYST-Beige mutant cells and inhibited L. amazonensis replication. Enlarged PVs appear to protect parasites from oxidative damage, since inhibition of nitric oxide synthase had no effect on L. amazonensis viability within large PVs, but enhanced their growth within LYST/Beige-induced small PVs. Thus, the upregulation of LYST/Beige in infected cells functions as a host innate response to limit parasite growth, by reducing PV volume and inhibiting intracellular survival.

The protozoan parasite Leishmania causes serious infections in humans throughout the world. After being inoculated into the skin through the bite of infected sandflies, the parasites enter host cells and replicate. The lysosome-like intracellular vacuoles where Leishmania amazonensis replicates expand dramatically as the infection progresses. Here we studied the impact of vacuole expansion on the ability of the parasites to survive and replicate inside host cells. We found that the host cell responds to infection with Leishmania amazonensis by upregulating expression of LYST/Beige, a gene that regulates the size of lysosomes and of parasite-containing vacuoles. The parasites replicated more efficiently in the large vacuoles formed in cells that have a mutation in LYST/Beige, whereas the same cells overexpressing functional LYST/Beige generated small vacuoles that were not able to sustain parasite growth. Drug treatments that reduced or enhanced the size of parasite-containing vacuoles had a corresponding effect on intracellular replication, demonstrating that large vacuoles provide a growth advantage to Leishmania amazonensis. Our results indicate that host cells respond to Leishmania infections by producing a protein capable of reducing vacuole size, as a strategy to inhibit parasite growth.

Effect of l-Arginine Analogs and a Calcium Chelator on Nitric Oxide (NO˙) Production byLeishmaniasp

Leishmania amazonensis, L. braziliensis and L. chagasi promastigotes were grown in the presence of L-arginine analogs such as Nomega-nitro-L-arginine methyl ester (L-NAME), NG-nitro-L-arginine (L-NNA) and D-arginine (an inactive L-arginine isomer), besides an intracellular calcium chelator [ethylene glycol-bis (beta-aminoethyl ether)-N,N,N',N'-tetra acetic acid; EGTA] to verify the importance of L-arginine metabolism and the cofactors for these parasites. The parasite's growth curve was followed up and the culture supernatants were used to assay nitric oxide (NO) production by the Griess reaction. The results showed a significant effect of L-arginine analogs on NO production by all Leishmania species studied, especially L-NAME, an irreversible inhibitor of the constitutive nitric oxide synthase (cNOS). When L. amazonensis promastigotes were pre-incubated with L-NAME, the infection range of the murine macrophages was lowered to 61% in 24 h and 19% after 48 h. These data demonstrated that the parasite NO pathway is important to the establishment of the infection.

Leonurus sibiricusinduces nitric oxide and tumor necrosis factor-α in mouse peritoneal macrophages

Using mouse peritoneal macrophages, we have examined the mechanism by which Leonurus sibiricus (LS) regulates nitric oxide (NO) production. When LS was used in combination with recombinant interferon-γ (rIFN-γ), there was a marked cooperative induction of NO production; however, LS by itself had no effect on NO production. The increased production of NO from rIFN-γ plus LS-stimulated cells was almost completely inhibited by pretreatment with pyrrolidine dithiocarbamate (PDTC), an inhibitor of nuclear factor κB. Furthermore, treatment of peritoneal macrophages with rIFN-γ plus LS caused a significant increase in tumor necrosis factor-α (TNF-α) production. PDTC also decreased the effect of LS on TNF-α production significantly. Because NO and TNF-α play an important role in immune function and host defense, LS treatment could modulate several aspects of host defense mechanisms as a result of stimulation of the inducible nitric oxide synthase.

Changes in the proteome and infectivity of Leishmania infantum induced by in vitro exposure to a nitric oxide donor

Leishmania species are protozoan parasites that exhibit an intracellular amastigote form within mammalian macrophages and an extracellular promastigote form inside the sandfly vector. The generation of nitric oxide (NO) upon activation of macrophages is surely the principal killing effector of intracellular amastigotes but little is known about the potential action of NO against the promastigote phase during its multiplication inside the digestive tract of the sandfly vector. Therefore, we have approached this issue by using an in vitro model to study the effect of an NO donor, 3-morpholinosydnonimine (SIN-1), on the proteome and infectivity of promastigotes of Leishmania infantum. Exposure of promastigotes to SIN-1 during its logarithmic growth phase caused a dramatic effect on parasite protein expression and viability, consequently killing about 60-70% of the promastigotes. The significant changes in the proteome included the over-expression of enolase, peroxidoxin precursors, and heat-shock protein 70 (HSP70), under-expression of 20S proteasome alpha 5 unit, and phosphomannomutase and induced expression of 3-hydroxy-3-methyglutaryl-CoA (HMG-CoA) synthase and prostaglandine f2-alpha (PGD2) synthase. Interestingly, promastigotes that resisted treatment showed enhanced infectivity to J774 macrophages in comparison to the controls. This finding together with the appearance of the PGD2S and an over-expression of HSP70 isoforms in treated promastigotes led us to speculate the existence of NO-mediated programmed cell death (PCD) events as a potential mechanism of population regulation and selection of properly infecting forms that predominantly operate on the promastigote stage.

Meglumine antimonate directly increases phagocytosis, superoxide anion and TNF-alpha production, but only via TNF-alpha it indirectly increases nitric oxide production by phagocytes of healthy individuals, in vitro

Leishmania has developed mechanisms to escape from immune defense of phagocytes by inhibiting microbicidal oxygen and nitrogen radicals. This work evaluated the influence of meglumine antimonate (Sb(V)) on the phagocyte functions involved in the defense against leishmania, through phagocytosis, reactive oxygen, nitrogen and TNF-alpha production in the absence or presence of the drug, in vitro. Meglumine antimonate increased the number of Saccharomyces cerevisiae ingested by monocyte and the percentage of these cells engaged in phagocytosis, which resulted in an increase of the monocyte phagocytic index by 158%. Meglumine antimonate also increased the number of S. cerevisiae ingested by neutrophil and the percentage of these cells engaged in phagocytosis, increasing the neutrophil phagocytic index by 219%. The median of percent reduction of NBT was significantly increased after treatment with this pentavalent antimony from 89.5% to 96.5%. Meglumine antimonate had no influence on nitric oxide production, but it significantly increased the mean+/-SEM production of tumor necrosis factor by 230%. However, monocytes incubated with TNF significantly increased NO production. This antimonial increased the phagocytic capacity of monocytes and neutrophils and enhanced superoxide anion production by phagocytes, which represent the first line of defense against the parasite. Furthermore, meglumine antimonate increased TNF, and via this cytokine, it may also indirectly increase NO production. Our data suggest that these immunomodulatory effects of meglumine antimonate may play a role in fighting leishmania and that meglumine antimonate provides the phagocytes with a mechanism that prevents leishmania from escaping immune defense.